1. Field of the Invention
The present invention relates to an arm mechanism in which translational motion for controlling position and rotational motion for controlling orientation are independently controlled. The arm mechanism of this invention can be applied to manipulators for manipulating cells and other fine operations, manipulators used in micro-assembly and other such manipulators.
2. Description of the Prior Art
The position and orientation of an end effector of a manipulator have to be controlled in order to manipulate an object with the end effector. In a conventional manipulator an end effector tip is provided on the end of an arm which has a serial link mechanism comprising a plurality of joints and link members extending from a base to the tip. The entire arm is driven to effect translational and rotational motions to set the position and orientation of the end effector. In this type of manipulator arrangement, there is interference between the end effector translational and rotational motions. Namely, changing the orientation of the end effector by rotating the end effector around one of the three axes of the orientation coordinate system affects the orientations (not to be changed) around the remaining two axes and the positions of the three axes of the rotation coordinate system. Similarly, changing the position of the end effector by translational motion of the end effector along one of the three axes of the position coordinate system affects the orientations around the three axes of the orientation coordinate system and the positions (not to be chagned) of the remaining two axes. This interference between translational and rotational motions reduces the accuracy of the end effector tip positioning and generated force. This has given rise to a demand for an arm mechanism that has independent control of position and orientation with no interference between translational and rotational motions.
Conventional arm mechanisms with independent control of position and orientation that have been devised include (1) a rotational arm mechanism that combines an absolute coordinate arm translational mechanism and a gimbal mechanism (pp 150-151 of the Collected Papers (V) of the 73rd General Meeting of the Japan Society of Mechanical Engineers (1996)); (2) a rotational arm mechanism that combines an absolute coordinate arm translational mechanism and a pantograph mechanism (Proc. of 1995 IEEE Int. Conf. on Robotics and Automation, Vol. 3, pp 3081-3088, (1995)); and (3) a mechanism that combines an absolute coordinate arm translational mechanism, a mechanism for rotating the arm without moving the tip, and a table translational and rotational mechanism (Robotics and Mechatronics Lectures of the Japan Society of Mechanical Engineers, Vol. B, pp 1386-1389, (1995)).
However, with the coordinate systems of these technologies being absolute coordinate systems, it is not always easy for an operator to ascertain the position and/or orientation of a target object or an end effector, making it difficult to achieve improvements in task efficiency and accuracy. In tasks such as the task of inserting a needle or rod in a hole, task efficiency and accuracy could be improved by using an end effector arrangement that enables coordinate systems to be established on the end effector that is always axially oriented toward the target point P on the object. However, since conventional manipulators are based on an absolute coordinate system, as described above, changing end effector orientation generates absolute coordinate system motion that differs from the end effector coordinate system motion required for the task, thwarting any improvement in task efficiency and accuracy.
A principal object of the present invention is to provide an arm mechanism with improved task efficiency and accuracy that offers improved accuracy of end effector tip positioning and generated force and facilitates operator comprehension of the position and orientation of a target object and the end effector.
Another object of the present invention is to provide an arm mechanism with improved task efficiency and accuracy that can maintain an end effector at a prescribed target point on an object.